Electromagnet Dimensions

[jheiss]

I am making a simple solenoid type electromagnet. I have 1000 feet of wire that I will be winding around a 1 inch diameter rod of soft iron . My question is are there optimal dimension ratios that I should consider? For example, how should the diameter compare to the height to achieve best results? Should the diameter be equal to the height? Or would it be better to have the diameter greater it is tall, or vise versa.
Also, would it be good to have the iron rod stick out of the coil or should I cut the ends of the rod flush with the coil? If it better to have the ends stick out, by how much? If there is anything else that would be good to know about winding your own electromagnet please do let me know. Thanks!

Jeff

 

[israelkk]

Is this a home project or a real engineering task?

 

[jheiss]

Just a personal home project.

 

[israelkk]

Since you already have the magnet wire then the minimal ohm resistace coil will give you the stronger magnet. Therefore if you know your power supply voltage then use a wire length that will give you the maximum current that you can allow (from safety reasons, coil heating reasons etc.).

A longer coil will have the minimal resistance with more turns (the larger the multiplication "no of turns x the current" the stronger the electromagnet). On the otherhand using the shortest rod will lower the iron magnetic resistance.

It would it be good to have the iron rod stick few mm out of the coil from both sides.

 

[hacksaw]

what field strength are you targeting?

 

[UKpete]

Just in passing, you know that the strongest force of attraction is achieved with the minimum amount of air in the magnetic circuit. For example, it is better to have an inverted U-shaped electromagnet rather than a simple bar if the aim is simply to pick up and hold, say, a steel plate.

The other point worth mentioning is that if you keep increasing the current (or more specifically, the number of turns x current) then eventually the iron will saturate and there is little point increasing the ampere turns further. It's a law of diminishing returns.